Push-pull chain actuator with reduced chain vibrations

ABSTRACT

A push-pull chain actuator ( 1 ) includes a housing with a chain exit/entry opening ( 4 ) and a sprocket ( 9 ) arranged to engage a push-pull chain ( 3 ). The sprocket ( 9 ) causes the polygon effect. The actuator includes a first chain guide part ( 10   a ) for guiding said push-pull chain ( 3 ) around the sprocket ( 9 ) and a second chain guide part (lob) for guiding said push-pull chain ( 3 ) at the correct angle between the chain exit/entry opening ( 4 ) and the sprocket ( 9 ). The second chain guide part ( 10   b ) is shaped and dimensioned to counteract the polygon effect. Alternatively, the second chain guide part ( 10   b ) can be shaped and dimensioned to reduce chain oscillations caused by the rollers ( 8   c ) engaging or disengaging the chain exit/entry opening ( 4 ) at the end of the second chain guide part ( 10   b ).

RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.12/995,921, which has a 35 U.S.C. §371(c) date of Mar. 7, 2011, whichclaims the benefit under 35 U.S.C. §371 of International PatentApplication No. PCT/DK2009/000128, filed Jun. 3, 2009, which claimspriority to European Patent Application No. 08010153.8, filed Jun. 4,2008, the contents of all of which are incorporated herein by referencein their entirety.

FIELD OF THE INVENTION

The present invention relates generally to actuators for push-pullchains, in particular to actuators with sprocket driven chains andguides for the push-pull chains used in these actuators.

BACKGROUND

A push-pull chain can be extended and retracted by an actuator basicallycomprising a driving sprocket and a housing for the push-pull chain. Thedriving sprocket engages the push-pull chain's rollers and drives it inthe desired direction. In order to keep these actuators compact thesprocket is provided with as few teeth as possible. However, typicallythe sprocket has five teeth since the so called polygon effect becomestoo large and disruptive for the actuator operation with fewer than fiveteeth.

It is a well known problem that the polygon effect even with five ormore teeth causes an irregular chain speed (assuming that the sprocketrotates with a substantially constant speed). The irregular chain speedresults in irregular forces on the chain and the actuator and on theobject to be actuated and causes noise, wear and reduced performance.Various attempts have been made in the prior art to overcome thisproblem. One of such attempts is disclosed in EP 1 227 056. In thisdocument it is proposed to use noncircular gear wheels that areconfigured to offset the polygon effect. Thus, the sprocket will notrotate with the constant speed, but rather with the fluctuating speed,whereby the fluctuations are configured and dimensioned to ensure thatthe resulting chain speed is constant. However, noncircular gear wheelsare more complicated to produce and cannot be obtained off the shelffrom mass production. Thus, this solution is relatively expensive.

Another issue with roller chain actuators is there need to be providedwith a chain exit guide that least supports two rollers at the time,otherwise the chain becomes instable. The links of the chain exit guideis a limiting factor in reducing the size of such actuators.

One way of reducing the noise has been discussed in U.S. Pat. No.4,827,668 that disclose a chain operator having a chain and a casinghaving a spaced first and a second exit opening. The chain is guided bya track from the first exit to the second. The casing also has a drivesprocket for driving the chain. This guide is used to steer the chaincorrectly so that the sprocket teeth do not jam into the chain linksthis to avoid unwanted noise. This apparatus is difficult to install asit is large, the push-pull chain is prone to rattle and the engine soundis uneven. As the casing is used to muffle the engine sound it needs tosubstantially completely enclose the actuator components and needs to beof a thick material to effectively silence the actuator.

As the push-pull chain is moved by the sprocket it goes from a linearmotion, through a circular motion and back to a linear motion again. Itis in this point of circular motion that the varying contact arisespartly due to the stiffness of the individual links.

Another problem is that as the push-pull chain is under push load, ase.g. in a push-pull chain being used to open a window, the push-pullchain is urged away from the sprocket due to the push force exerted onthe push-pull chain by the load. This effect may cause the push-pullchain to disengage the sprocket completely or partly leading to noiseand partially or completely impaired function.

To overcome this, a first guide surface is used to guide the push-pullchain along the sprocket and prevents the push-pull chain from movingaway from the sprocket and keeps the push-pull chain in close relationto the sprocket.

Actuators having guide surfaces such as these, however, still make a lotof noise and the push-pull chain is prone to rattle, in particular dueto a swaying movement of the push-pull chain in the vicinity of thechain exit caused by the interaction of the sprocket with the push-pullchain.

In a small actuator a small sprocket is required and this leads to alimited number of teeth for a robust push-pull chain. Due to the sizeand geometry of the teeth only 1 to 2 chain links are in contact withthe sprocket. For a sprocket with 5 teeth usually 1-1% chain links arein contact with the sprocket at any given moment in time.

As the push-pull chain progresses along the sprocket it will first comein contact with the sprocket, follow it and then leave it. Doing so therollers 8 b of the push-pull chain are being engaged by different partsof the sprocket, i.e. the teeth of and the recesses in-between them. Asthe recesses are closer to the centre of the sprocket than the teeth,the sprocket has a polygonal geometry, and when the sprocket is rotatingwith a steady speed the resulting chain velocity is varying. Also theforce transmitted from the sprocket to the push-pull chain will beun-even in both direction and amplitude. This is especially apparentwhen the push-pull chain is put under load and thereby urged away fromthe sprocket. Due to this polygon effect the push-pull chain will leavethe actuator at the chain exit opening with varying angle, and thepush-pull chain will sway or oscillate. For a sprocket only having asmall number of teeth this problem becomes more apparent as thepolygonal effect becomes more prominent as only a few links are incontact with the sprocket at any time which causes the effect of asingle tooth to dominate the movement of the link and since the changesin the effective radius of the sprocket become more prominent. Thiscauses the push-pull chain to move erratically which causes it to swayas it leaves the actuator. This swaying movement reduces the push-pullchain stability under push load as it increases the risk of thepush-pull chain assuming a shape in which it is prone to collapse.Furthermore, rattling noise is generated as the push-pull chain clangsagainst the actuator and other parts and also by the push-pull chainitself. Especially for push-pull chains the stability is an importantissue.

Another problem associated with chain actuators are the chainoscillations that are caused by the rollers leaving or entering thechain exit/entry opening. A transverse force is unavoidably applied tothe chain and each time a roller enters or leaves the chain exit/entrythere is a transverse movement of the roller that is getting into or outof contact with the chain guide. Theoretically, this problem could bereduced if the actuator and the chain could be constructed without anyplay or backlash between the rollers and the chain guide and between therollers and the pins of the chain. However, in practise a certain amountof play is required and has to be accepted. The resulting chainoscillations result in noise and war and reduced performance and aretherefore undesirable.

DISCLOSURE OF THE INVENTION

It is an object of this application to provide a push-pull chainactuator that overcomes or at least reduces the problems relating to thepolygon effect stated above or in other words to produce a push-pullchain actuator that keeps the push-pull chain more stable, reduces thenoise, produces a smooth operation, is easy to install and with areduced variation of the angle in which the push-pull chain leaves theactuator.

By realizing that the polygon effect can be neutralized by providing aspecial shape for the chain exit guide between the sprocket and thechain exit/entry opening, the above object could be achieved in anunexpected manner.

Thus, this object is achieved by providing a push-pull chain actuatorcomprising a housing with a chain exit/entry opening, a push-pull rollerchain with an open back, a sprocket arranged to engage the rollers ofthe push-pull chain, whilst a portion of the chain is guided around thesprocket, the sprocket causing a polygon effect during operation, achain guide comprising: a first arc shaped chain guide part for guidingthe portion of the push-pull chain around the sprocket by the rollers ofthe chain being guided by the first arc shaped chain guide, a secondchain guide part for guiding the push-pull chain in a predeterminedexit/entry direction between the sprocket and the chain exit opening bythe rollers of the chain being guided by the second chain guide, whereinthe chain guide is shaped and dimensioned to neutralize or at leastreduce the polygon effect of the sprocket on the push-pull chain.

By guiding the push-pull chain in a way that neutralizes or at leastreduces the effects of the polygonal effect of the sprocket thepush-pull chain can be made to leave the actuator at a steady speed andload, causing less wear and noise. Further, this measure had theunexpected side effect that the angle at which the chain leaves theactuator varies less when the chain is moving and thus, the actuator canbe constructed with a build in chain exit/entry angle closer to 90°,resulting in a higher push load bearing capacity of the chain.

The chain exit can be constructed shorter because the exit guide extendsinto the arc shaped guide that guides the chain around the sprocket. Ashorter exit guide allows for a reduced width of the housing andtherewith a slimmer actuator.

Preferably, the second chain guide part causes the rollers to follow ameandering path between the chain exit and the sprocket.

The second the chain guide part may comprise a path for the rollersformed by a series of interconnected arc shaped sections.

The geometrical centres of the arc shaped sections may be on the sameside of the chain as the geometrical centre of the first chain guidepart.

The geometrical centres of the arc shaped sections maybe substantiallyarranged on a line extending parallel to the predetermined chainexit/entry direction. The line may coincide with the centre of thesprocket.

The arc shaped sections in the series may have a radius that issubstantially identical to the radius of the path defined by the firstchain guide part.

The transition between the arc shaped sections is preferably rounded offor rendered smooth.

It is another object of the invention to provide a chain guide for apush-pull chain actuator, the chain guide comprising a first arc shapedchain guide part for guiding the portion of the push-pull chain aroundthe sprocket by the rollers of the chain being guided by the first arcshaped chain guide, a second chain guide part for guiding the push-pullchain in a predetermined exit/entry direction between the sprocket andthe chain exit opening by the rollers of the chain being guided by thesecond chain guide, characterised in that the chain guide is shaped anddimensioned to neutralize or at least reduce the polygon effect of thesprocket on the push-pull chain.

it is another object of the invention to provide a method forneutralizing or at least reducing the polygon effect of a sprocket on apush-pull chain in a chain actuator, comprising: providing a chain guidefor guiding the chain around the sprocket of the actuator and betweenthe sprocket and a chain exit/entry opening, by providing a chain guidethat defines a meandering path for the push-pull chain between thesprocket and the chain exit/entry opening that neutralizes or at leastreduces the polygon effect.

it is another object to provide a chain actuator in which the chainoscillations caused by the rollers engaging or disengaging the chainexit/entry opening.

This object is achieved by providing a push-pull chain actuatorcomprising a housing with a chain exit/entry opening, a push-pull rollerchain with an open back and a given chain pitch between the pins thatconnect the links of the chain and support the rollers, a sprocketarranged to engage the rollers of the push-pull chain whilst a portionof the chain is guided around the sprocket, a chain guide comprising: afirst arc shaped chain guide part for guiding the portion of thepush-pull chain (3) around the sprocket by the rollers of the chainbeing guided by the first arc shaped chain guide, a second substantiallystraight chain guide part for guiding the push-pull chain in apredetermined exit/entry direction between the sprocket and the chainexit opening by the rollers of the chain being guided by guide surfacesof the second chain guide part, wherein the second substantiallystraight chain guide part is provided with a local deviation from astraight line, the local deviation reaching a maximum approximately onechain pitch length distance from chain exit opening and the deviationurging the rollers of the chain to move transversely towards the side ofthe second chain guide on which the sprocket is arranged when therollers pass the deviation.

Preferably, the size of the maximum deviation is adjusted to the play ortolerance between the rollers and the pins and the play or tolerancebetween the rollers and the guide surfaces of the second chain guidepart.

The deviation can be formed by a step formed in the guide walls of thesecond chain guide part.

The deviation may comprise a deviation portion that guides the rollersfrom the substantially straight extend of the second chain guide parttowards the point or area of maximum deviation and a deviation portionthat guides the rollers from the point or area of maximum deviation backto the substantially straight extend of the second chain guide part.

An actuator having a guide surface such as any of the above describedwill have the benefits of using less power, making less engine noise andless rattling as the guide cam steadies the push-pull chain.

An actuator such as described above can advantageously be used for awindow system using a push-pull chain to open and close a window as thisfield has a high requirement for low noise levels, reliable operation,easy installing and low power consumption.

The above described also applies to push-pull chain actuators that arenot driven by a motor as when the driving sprocket is wound by hand.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following detailed portion of the present description, theinvention will be explained in more detail with reference to theexemplary embodiments shown in the drawings, in which

FIG. 1 is a cross-sectional view though an actuator according to anembodiment of the invention,

FIG. 2 is a detailed view of a section of FIG. 1,

FIG. 3 is diagrammatic view of a chain guide for use in an actuatoraccording to the invention,

FIGS. 4 to 6 are a series of views on the chain guide, chain andsprocket of the actuator of FIG. 1 illustrating the movement of thechain through the chain guide,

FIGS. 7 to 9 are diagrammatic views of a chain guide according otherembodiments of the invention, and

FIG. 10 is a schematic drawing to illustrate misalignment of the chaindue to tolerances forces acting on the chain.

DETAILED DESCRIPTION OF THE DRAWINGS

In the following detailed description, the invention will be describedby embodiments.

With reference to FIGS. 1 and 2 a push-pull chain actuator 1 accordingto an embodiment of the invention is shown. The actuator has a housing 5and is provided with a push-pull chain 3 and with an electric drivemotor 15. The housing 1 is provided with the chain magazine 25, which isempty in FIG. 1 since the push-pull chain 3 is shown in its fullyextended position. For practical reasons the push-pull 3 chain has notbeen drawn in its full length, but it is understood that the push-pullchain 3 can extend much further from the actuator 1 than shown in FIG.1.

The actuator 1 has a sprocket 2 having a number of teeth 9 (in thisembodiment 5 teeth) and a chain exit opening 4 adjacent to the sprocket2 through which the push-pull chain 3 can extend from the actuator 1.The actuator 1 has a housing 5 for receiving the push-pull chain 3. Anelectric drive motor 15 drives the sprocket 2 via a reduction gear thatincludes worm (which cannot be seen in this cross-section), a wormwheel16 and further reduction gears 18 in an as such well known manner.According to another embodiment (not shown) the actuator is manuallypowered.

The push-pull chain 3 includes a plurality of inner links 7 a and outerlinks 7 b that are connected by drive pins 8 a around which the links 7a,7 b can move in relation to each other so that the push-pull chain 3is at least partially flexible. The opposing inner links of a pair areconnected by bushings 8 c. The bushings 8 c are provided with rollers 8b to minimize the friction caused while being engaged by the sprocket 2.The chain can freely bend from a configuration in a straight line in onedirection. However, from the straight configuration the push-pull chain3 can only bend to a limited extent in the opposite direction to providethe required stiffness for the push action in an as such well knownmanner. The stiffness in the one direction is obtained in a well knownmanner through the shape of the inner and outer links 7 a,7 b, so thattheir ends abut when the chain 3 is bend in the “opposite” direction.Both sides of the chain 3 are open (as opposed to some types ofpush-pull chains that have a closed back) so that the rollers 8 b areaccessible for contact with guide surfaces on both sides of thepush-pull chain 3. In FIG. 2 the internal extremity 19 of the push-pullchain 3 is visible with the push-pull chain 3 being in its fullyextended position.

The sprocket 2 has a number of teeth 9. The higher the number of teeth 9the smaller angular distance between them which leads to either a largersprocket 2 or thinner teeth 9 and/or corresponding chain dimensions i.e.a weaker push-pull chain. To ensure a robust and load bearing structurethe sprocket 2 should have as few teeth 9 as possible. However, a largeangle between the teeth 9 worsens the so called polygon effect thatresults in an uneven chain speed and correspondingly uneven load, bothbeing undesirable effects. A sprocket 2 with less than four teeth 9leads to a very uneven operation as the angular distance between theteeth get so large that the polygon effect gets very prone. With morethan 5 to 6 teeth the sprocket becomes bigger and the push-pull chain 3thinner and thereby weaker if the same dimensions for the housing are tobe kept.

Good results have been achieved with a sprocket having five teeth 9 foractuators used to open close windows, doors and the like. The polygoneffect is still noticeable, but the chain will move reasonably smooth.

As the push-pull chain 3 is driven by the sprocket 2 it undertakes firsta substantially linear motion that is changed into a semi-circular orangular motion around the sprocket 2 and finally another substantiallylinear motion as it extends from the actuator 1. Due to this theactuator 1 can be installed along narrow ledges, window sills and thelike as the push-pull chain 3 does not extend linearly all the way, i.e.to the back of the actuator and away from a ledge or the like.

FIGS. 2 and 3 illustrate a chain guide of the actuator of FIG. 1 ingreater detail. The chain guide ensures that the push pull chain 3follows the correct path of movement between the chain magazine 25 andthe chain exit/entry opening 4, For this purpose, the chain guide isprovided with guide surfaces on which the rollers 8 b run when thepush-pull chain 3 moves through the chain guide. Thus, the push-pullchain 3 is guided by contact between the rollers 8 b and the guidesurfaces of the chain guide.

A first chain guide part 10 a ensures that the push-pull chain 3 followsan arc shaped path around a portion of the sprocket 2 so that thesprocket 2 can engage the rollers 8 b and transmit the load of thepush-pull chain 3 to the sprocket 2. When the push-pull chain 3 isplaced under push load the chain links 7 a,7 b are subjected to a forceurging them away from the sprocket 2. This load can be the weight orinertia of a window (not shown) that is being opened, dosed ormaintained in an open position by the push-pull chain 3 using theactuator 1. The first chain guide part 10 a includes a radially outerarc shaped guide surface 20 a that serves to guide the chain links 7 a,7b around the sprocket 2 and a radially inner guide surface 21 a thatwill need to provide no or little guiding since the guiding of the chainin the radially inner direction will be provided by the sprocket 2. Theguide surface 20 a is arranged on a first guide cam 11 and the guidesurface 21 a is provided on a second guide cam 13. The first guide cam11 and the second guide cam 13 form together the chain guide. The firstchain guide part 10 a extends between interrupted lines Q and W forapproximately 90°. The first chain guide part 10 a is arranged to be incontact with the rollers 8 b of the chain and to keep the rollers 8 bdose to the sprocket 2 and thereby guide the push-pull chain 3 aroundthe sprocket 2 also when the push-pull chain 3 is under push load.

A second chain guide part 10 b serves to guide the push-pull chain 3between the sprocket 2 and the chain exit/entry opening 4, and inparticular to ensure the correct exit/entry direction of the chain toprovide the required stability against push loads. The second chainguide part 10 b is provided with two opposite guide surfaces: a firstexit/entry guide surface 20 b that is formed on the first guide cam 11and a second exit/entry guide surface 21 b that is formed on the secondguide cam 13. The second chain guide part 10 b extends betweeninterrupted line X the chain exit/entry opening 4 (FIG. 5). The secondchain guide part 10 b defines a meandering path for the chain. Theresulting meandering movement of the rollers 8 b that can be best seenin FIGS. 4 to 6 counteracts or at least reduces the polygon effect. Thedetails of the second chain guide portion 10 b will be described ingreater detail further below.

A third chain guide part 10 c serves to guide the chain between thechain magazine and the first chain guide part 10 a, The third chainguide part 10 c is provided with opposing guide surfaces 20 c and 21 cfor ensuring that the chain travels correctly between the sprocket 2 andthe chain magazine.

In order to make use of the push-pull chain's 3 supportive propertiesthe actuator is designed so that the push-pull chain 3 extends at anangle that slightly exceeds a straight angle from the actuator 1 so thatthe push-pull chain 3 is urged into its stable orientation. This desiredor correct angle is indicated in FIGS. 4-6.

During operation the irregular shape of the chain in combination withthe polygon effect causes in conventional actuators with anon-meandering exit guide (the part of the chain guide that correspondsto the second chain guide part) fluctuations of the actual chain anglefrom the design angle. Typically the chain angle variations in theconventional chain guides is typically ±2° from the angle with which theexit guide is constructed. Since the chain angle should under nocircumstances become less than 90°, the conventional actuators havetypically been constructed with an angle of 93° or more so that the willnot lead to fluctuations that cause the actual chain angle to fall below91°. The meandering path on the second chain guide part (also calledchain exit guide) 10 b annihilates or at least greatly reduces thefluctuations of the angle of the push pull chain 3 leaving the actuator1 completely or at least substantially and therefore the chain thataccording to the present invention can be constructed with an inbuiltangle as low as 91.5°. As is illustrated in FIGS. 4 to 6, thefluctuation of the chain angle with the meandering exit guide or secondchain guide part 10 b is only ±0.5°, i.e. the chain changes between 91°and 92° with an inbuilt chain angle of 91.5°. The building chain anglecan with meandering chain path according to the invention be kept closerto 90° which means that the chain support higher push loads. Further,the reduction in swaying movement of the push pull chain 3 will reducethe amount of noise and rattling calls by the actuator 1.

The reduction or neutralization of the polygon effect further reducesthe amount of noise produced by the actuator 1 in operation since themovement of the chain angle of the object to be moved will be smooth andwithout fluctuations.

In order counteract or off-set the polygon effect the second chain guidepart 10 b can be meandering undulating, lobed, have protrusions, consistof curved portions or deviate from a straight line or a constant radiuscurve in various ways. In order to provide the meandering movement ofthe chain the second chain guide part 10 b or exit/entry guide needsguide surfaces on both sides of the chain/rollers. Theoretically, themathematically optimal form for completely neutralizing the polygoneffect is by shaping the second chain guide part 10 b as a series ofinterconnected arc sections, the arc sections having a radius that isequal to the radius of the first chain guide part 10 a and the arcsections hang an angular extend equal to the angle between the teeth ofthe sprocket. With a sprocket with five teeth this gives a maximumangular extend of the individual arc sections of 72° (the same angulardistance as the angular distance between the teeth of the sprocket). Thearc sections could be made smaller than 72° but the neutralizing effectwill be less effective. It should be noted that the “first” arc sectionat the sprocket extends halfway into the “conventional” substantially90° arc section that forms the first chain guide part 10 a. Thus, asshown in FIG. 3, it appears that the first arc section of the secondpart of the chain guide 10 b is only 36°, this is because the arc aroundthe sprocket 2 cannot be extended further than 36° over the interruptedline marked X. The next arc sections are in the embodiment of FIG. 3 areeach 72° and have a radius identical to the radius of the first chainguide part 10 a, Also the first 36° arc section has a radius that issubstantially identical to the radius of the first chain guide part 10a.

The geometrical centres of said arc shaped sections of the second chainguide part 10 b are on the same side of the chain 3 as the geometricalcentre of the first chain guide part 10 a.

The geometrical centres of said arc shaped sections are substantiallyarranged on a line (indicated by the interrupted line marked Y)extending parallel to the predetermined chain exit/entry direction. Theline marked Y coincides with the centre of the sprocket 2.

Thus, the chain guide shown in FIG. 3 is constructed in accordance withthe mathematically optimal way to fully neutralize the polygon effect.However, in practice the sharp transitions between the arc sections, atthe guide surfaces 20 b and 21 b prevent smooth rolling of the rollers 8b, and in practical embodiments the sharp transitions will be roundedoff.

The second chain guide part 10 b needs to extend for a length thatensures that at least two rollers 8 b are supported at any time by thesecond chain guide part 10 b (is this is also nicely illustrated inFIGS. 4 to 6). This means that the second chain guide part 10 b mustextend for at least 2.5 times the pitch (pitch between the drive pins 8a) of the chain 3. This requirement is fulfilled with two arc sectionsof 72° for an actuator with a five tooth sprocket. The reduction oflength of the chain exit guide 10 b can be explained as follows. It isnoted that the first arc shaped section of the exit guide 10 b extendshalfway (for 36° with arcs that are 72°) into the first chain guide part10 a, and thus the exit guide actually starts already at the interruptedline indicated W. Thus, the chain exit guide is partially wrapped aroundthe sprocket and is drawn closer to the sprocket resulting in the exitopening being located closer to the sprocket and the width of theactuator being reduced when compared to an actuator with a conventionalchain exit guide. An actuator with a reduced width is advantageous sincesuch an actuator can be constructed slimmer and therefore easier tomount into a window frame or the like

Of course it is possible to use a longer chain exit guide 10 b with morethan two arc sections if desired.

It should be noted that the guide surfaces can be subdivided intosmaller surfaces working together to steady the push-pull chain 3 orcombined into one longer guiding surface that renders it easier toinstall them

The guide surfaces 20 a,20 b,20 c,21 a,21 b,21 c can be designed toeither only abut a joints or rollers 8 b under and/or over a sprockettooth 9 or have a slit through which the sprocket tooth 9 can passdepending on the length of the sprocket tooth 9 in relation to the widthof the drive pin 8 a, This also makes it possible to arrange the secondguide cam 13 on top of and under the sprocket 2 and use it as asupportive member for the sprocket 2.

In the final portions of both guide cams 11 and 13 the second and thirdguiding surfaces 10 b and 10 a are lobed or undulating or having curvedportions to counteract the polygon properties of the sprocket 2interacting with the chain links 7 a,7 b.

FIG. 7 illustrates another embodiment of the invention. This embodimentrelates to a chain actuator that is essentially identical to the chainactuator described above, except for the second chain guide part 10 b.In this embodiment the aim of the chain guide is to reduce chainvibrations that are common in conventional chain actuators. These chainvibrations are caused by the effect of the rollers 8 c leaving(disengaging) the chain guide at the exit/entry opening 4 (when theactuator 1 is extending) or of the rollers 8 c entering (engaging) thechain guide at the exit/entry opening 4 (when the actuator 1 isretracting) and the transverse movement of the rollers 8 c whenentering/exiting the chain guide. The chain 3 is always slightly bentbeyond the configuration in which it is straight (in one direction thechain cannot bend further than slightly beyond this configuration) sothat the (push pull) chain 3 can act as a push rod. The bending beyondthe straight line configuration creates a transverse force on the chainlinks 7 a,7 b in the second chain guide part 10 b and this force urgesthe chain links 7 a,7 b to misalign in the second chain guide part 10 b.This misalignment is possible due to a certain amount of (required) playor backlash between the rollers 8 b and the guide surfaces of the secondchain guide part 10 b and between the pins 8 a and the rollers 8 b(there can be bushings 8 c provided between the pins 8 a and the rollers8 b). This play and misalignment is illustrated in an exaggerated formin FIG. 10.

Thus, a transverse force acts on the rollers 8 b when they leave orenter the chain exit/entry opening 4. The transverse force incombination with the play between the rollers 8 c and the second chainguide part 10 b and between the rollers 8 c and the pins 8 a creates anoscillating transverse movement of the rollers 8 c and of the chain 3.This oscillating transverse movement (chain vibration) in conventionalchain actuators is largest at the chain exit/entry 4 and causes the partof the chain 3 that is not received in the actuator 1 to oscillate whenthe chain 3 is moving, The vibrations and sound associated with theseoscillations can be detrimental to the actuator 1, and any componentsdirectly or indirectly connected therewith. Further, the noise generatedby the oscillations can be experienced as disturbing.

The chain guide shown in FIG. 7 removes or at least reduces thisoscillating transverse movement. Hereto, the second chain guide part 10b, which is essentially straight, is provided with a deviation 30 fromthe straight line. The deviation 30 has a predetermined maximum that isarranged approximately one chain pitch “P” length distance from thechain exit. The location of the maximum deviation is indicated by theinterrupted line in FIG. 7. The size of the maximum deviation isadjusted to the play or tolerance between the rollers 8 c and the pins 8a and the play or tolerance between the rollers 8 c and the guidesurfaces of the second chain guide part 10 b. The deviation is in thedirection of the side of the chain guide at which the sprocket islocated.

Due to the deviation 30 one of the rollers 8 c of the chain 3 is forcedto move in a transverse direction to an extend that substantiallycorresponds to the maximum of the deviation 30 and thereby changes theorientation of the last/first chain link 7 a,7 b in the chain guide. Thechanged orientation places the chain links 7 a,7 b near the chainexit/entry opening 4 in an optimum orientation for reducing and evenremoving and transverse chain movement at the chain exit/opening 4.

The deviation 30 includes in the embodiment of FIG. 7 two parallel setsof straight guide surface sections of the second chain guide. Each ofthese sets is arranged at an angle with the overall straight extend ofthe second chain guide part 10 b. Seen in a chain extension direction,one set of straight guide surfaces guides the rollers 8 c to the maximumdeviation and the other set of straight guide surfaces guides therollers 8 c from the maximum deviation back to the straight extend ofthe second chain guide part 10 b.

FIG. 8 illustrates another embodiment of the invention that isessentially identical to the embodiment of FIG. 7, except that thedeviation has a different shape. In the embodiment of FIG. 8 thedeviation is formed by two curved sections in the guide surfaces of thesecond chain guide part 10 b.

FIG. 9 illustrates yet another embodiment of the invention that is alsoessentially identical to the embodiment of FIG. 7, except that thedeviation has a different shape. In the embodiment of FIG. 9 thedeviation is formed by stepped sections in the guide surfaces of thesecond chain guide part 10 b.

Even though the embodiments have been described focusing on theoperation when the chain is extended from the actuator it should beunderstood that the corresponding situation is present also when thechain is retracted.

It should be understood that the actuator as described above can also beused beneficially for actuators that are manually operated.

It should be understood that the embodiments can be combined.

The term “comprising” as used in the claims does not exclude otherelements or steps. The term “a” or “an” as used in the claims does notexclude a plurality

The reference signs used in the claims shah not be construed as limitingthe scope.

Although the present invention has been described in detail for purposeof illustration, it is understood that such detail is solely for thatpurpose, and variations can be made therein by those skilled in the artwithout departing from the scope of the invention.

The invention claimed is:
 1. A push-pull chain actuator comprising: ahousing with a chain exit/entry opening, a push-pull roller chain withan open back, said chain comprising a plurality of pairs of inner linksand pairs of outer links that are connected by drive pins with rollersthat are disposed between opposing inner links of said pairs of innerlinks, a sprocket arranged to engage said rollers of the push-pullroller chain, whilst a portion of the push-pull roller chain is guidedaround the sprocket, said sprocket causing a polygon effect duringoperation, a chain guide comprising: a first arc shaped chain guide partfor guiding said portion of said push-pull roller chain around saidsprocket by the rollers of the push-pull roller chain being guided bythe first arc shaped chain guide part, a second chain guide part forguiding said push-pull roller chain in a predetermined exit/entrydirection between the sprocket and an chain exit opening by the rollersof the push-pull roller chain being guided by the second chain guidepart, wherein said second chain guide part is shaped and dimensioned toneutralize or at least reduce variations in chain speed caused by thepolygon effect of the sprocket on the push-pull roller chain byincluding a deviation from a straight line that causes the rollers tofollow a meandering path between the chain exit opening and thesprocket.
 2. The actuator according to claim 1, wherein the second chainguide part comprises a path for said rollers formed by a series ofinterconnected arc shaped sections.
 3. The actuator according to claim2, wherein geometrical centres of said arc shaped sections are on a sameside of the push-pull roller chain as geometrical centre of the firstchain guide part.
 4. The actuator according to claim 3, wherein thegeometrical centres of said arc shaped sections are substantiallyarranged on a line (Y) extending parallel to the predetermined chainexit/entry direction.
 5. The actuator according to claim 4, wherein saidline (Y) coincides with a centre of the sprocket.
 6. The actuatoraccording to claim 2, wherein the arc shaped sections in said serieshave a radius that is substantially identical to a radius of the pathdefined by the first chain guide part.
 7. The actuator according toclaim 2, wherein a transition between said arc shaped sections isrounded off or rendered smooth.
 8. The actuator according to claim 1,wherein said deviation from a straight line reaches a maximum deviationone chain pitch length distance from the chain exit opening and saiddeviation urges the rollers of the push-pull roller chain to movetransversely towards a side of the second chain guide on which thesprocket is arranged when the rollers pass the deviation.
 9. Theactuator according to claim 8, wherein a size of the maximum deviationis adjusted to a play or tolerance between the rollers and pins and theplay or tolerance between the rollers and guide surfaces of the secondchain guide part.
 10. The actuator according to claim 8, wherein saiddeviation is formed by a step formed in guide walls of the second chainguide part.
 11. The actuator according claim 10, wherein said deviationcomprises a deviation portion that guides the rollers from asubstantially straight extend of the second chain guide part towards apoint or area of maximum deviation and a deviation portion that guidesthe rollers from the point or area of maximum deviation back to thesubstantially straight extend of the second chain guide part.
 12. Theactuator according to claim 3, wherein a transition between said arcshaped sections is rounded off or rendered smooth.
 13. The actuatoraccording to claim 4, wherein a transition between said arc shapedsections is rounded off or rendered smooth.
 14. The actuator accordingto claim 5, wherein a transition between said arc shaped sections isrounded off or rendered smooth.
 15. The actuator according to claim 6,wherein a transition between said arc shaped sections is rounded off orrendered smooth.
 16. The actuator according to claim 2, wherein saiddeviation from a straight line reaches a maximum deviation one chainpitch length distance from chain exit opening and said deviation urgesthe rollers of the push-pull roller chain to move transversely towards aside of the second chain guide on which the sprocket is arranged whenthe rollers pass the deviation.
 17. The actuator according to claim 3,wherein said deviation from a straight line reaches a maximum deviationone chain pitch length distance from chain exit opening and saiddeviation urges the rollers of the push-pull roller chain to movetransversely towards a side of the second chain guide on which thesprocket is arranged when the rollers pass the deviation.
 18. Theactuator according to claim 4, wherein said deviation from a straightline reaches a maximum deviation one chain pitch length distance fromchain exit opening and said deviation urges the rollers of the push-pullroller chain to move transversely towards a side of the second chainguide on which the sprocket is arranged when the rollers pass thedeviation.
 19. A chain guide for a push-pull chain actuator, said chainguide comprising: a first arc shaped chain guide part for guiding aportion of said push-pull chain around a sprocket by rollers of thepush-pull chain being guided by the first arc shaped chain guide, and asecond chain guide part for guiding said push-pull chain in apredetermined exit/entry direction between the sprocket and a chain exitopening by the rollers of the push-pull chain being guided by the secondchain guide, wherein said second chain guide part is shaped anddimensioned to neutralize or at least reduce a polygon effect of thesprocket on the push-pull chain by including a deviation from a straightline that causes the rollers to follow a meandering path between thechain exit opening and the sprocket.